Hair is an intricate and dazzling romp through the Sixties (Picture: Claire Bilyard)

‘It’s given me a whole new impression of my mother!,’ one young audience member said in the hippy-themed pop-up bar before the show began. Standing closeby I spot a woman in her Seventies or Eighties wearing a special tie die dress for the occasion.

Hair’s main draw is clear – the musical naturally draws the generations together through its gutsy, disruptive themes of revolution.

I suppose a cynic might say that of course it does. Hair, after all, is hardly a difficult sell: a sexually and politically charged musical about the 1960s, about Flower Power, and about drug-infused hippy culture, with a script updated for the modern age, it’s hardly hard work.

There are euphoric moments (Picture: Claire Bilyard)

But this intricately dazzling production goes so much further than its familiar and alluring premise.

Premiering off-Broadway in 1967, Hair transferred to Broadway in 1968, and in the time in-between – to give some cultural context to the mood of the time – Martin Luther King was assassinated. The musical tells the liberating, and liberated, story of a group of young people in New York’s East Village who come together as a tribe. Living an earthly existence on the fringes of society, they question the ethical bedrock underpinning us all.

The war in Vietnam acts as backdrop to themes which span ethnic diversity, Black Lives Matter, the environment, women’s rights and LGBT issues. The Vaults, the subterranean cavernous theatre space below Waterloo station, feels made for an edgy show like this. Dingy and underground, and decorated with thousands of handmade brightly coloured hippy tassels, it’s as fragile, makeshift and alternative as the lives and conquests of the tribe members.

The singing is spectacularly ingrained into the plot (Picture: Claire Bilyard)

All things considered, Jonathan O’Boyle’s production is theatrical gold. The ferocious might of the tribe is best communicated through deft physical theatre: ambitious, immersive choreography combines with choral harmonies that sound Biblical against Maeve Black’s vividly colourful, Utopian set.

Director O’Boyle stages things like psychedelic drug use, and being killed on the Front Line at war with combined audio-visual excellence: his scenescapes feel emblematic, like they should transcend the show as lasting depictions of both war and drug culture.

Rebellion is at the heart of the plot (Picture: Claire Bilyard)

As the tribe pop pills, choreographer William Whelton makes full use of the space to get as close to a staged hallucination as I can imagine is possible (using acting that is, not naff technological cheats), and on the Front Line, figures drop like dead weights; their eyes unfocused and hazy.

The singing and dancing has all been brought up to date: Trump even has a haunting, though not unexpected, cameo to reinforce the sad reality that the concerns of the Tribe still haunt us today, on the 50th anniversary of this production.

Hair is staged in-the-round, with the audience either side, at The Vaults (Picture: Claire Bilyard)

The two-act show energetically squeezes in over 40 songs in just shy of two-and-a-half hours, and the 14-strong cast, as acrobatic as they are vocally nimble, never seem to need a moment off. They possess never-ending energy as they strip, frolic and fight for their rights.

We’re not in the business of spoiling triumphant closing numbers, so let’s just say all would-be revolutionaries get far more than a dancing in the isle moment when this spectacular comes to a close. You’ll feel closer to your mother, lover – or the stranger in the seat next to you – than you’d ever have imagined.